This application is directed to the field of telephony, and more particularly to the field of cordless telephones.
A cordless telephone comprises a base unit, which is typically stationary and linked to a telephone network, and a handset, which can roam relative to the base unit within a predefined area limited by the range of an RF link between the base unit and the handset. The base unit is typically linked to the network, such as the public switched telephone network, via an interface, such as a telephone line interface.
During an exemplary telephone call, analog audio signals are communicated between the base unit and the network via the telephone line interface. In a digital cordless telephone, received analog signals from a far end party to a telephone call are conventionally converted in the base unit to digitally encoded speech samples for digital communication over the RF link between the base unit and the handset. Conversely, digitally encoded speech samples representing near end speech signals from a party speaking into the handset are converted to analog signals in the base unit for transmission to the far end party via the telephone line interface and the network.
Typically, the digital speech samples transmitted between the base unit and the handset are encoded by an encoding unit, also known as a vocoder, to reduce the bandwidth required to transmit the samples over the RF link. An exemplary vocoder may employ the coding technique known as Adaptive Differential Pulse Code Modulation (ADPCM), which is known to one of skill in the art. The encoded speech samples are also typically transmitted in frames, with each frame including a predetermined number of digital bits associated with the encoded speech samples, and other digital words or bits associated with overhead functions, such as a preamble, error correction, etc.
The RF link between the base unit and the handset is also typically employed to transmit non-speech data therebetween. Examples of non-speech data include display related information transmitted to the handset, such as to instruct the handset to display Caller ID data, ring commands or page commands transmitted to the handset to cause it to produce specific audible sounds, and key press information transmitted to the base unit to inform the base unit of specific handset keys being activated, or to instruct the base unit to implement a particular function associated with the activated keys.
Conventionally, a technique known as the xe2x80x9cblank and burstxe2x80x9d method is employed for transmitting this non-speech data. According to this method, a control portion of a frame informs the receiving device (i.e., the handset if the base unit is transmitting; or the base unit if the handset is transmitting) that the data portion of the frame contains non-speech data instead of speech data, and the control portion also informs the receiving device of the type of non-speech data. The receiving device thus handles the non-speech data appropriately.
There is a disadvantage, however, in that the blank and burst frame is transmitted in the midst of real-time speech frames associated with an on-going telephone call. This results in an interruption that causes a slight degradation to the speech quality, which may be perceived by the parties engaged in the telephone call, especially if the non-speech frame is transmitted in close proximity to other non-speech frames. There is a need, therefore, for a non-speech data transmission approach that is adaptive to minimize any adverse impact to on-going speech transmissions.
This need is met by a method of transmitting digital data between a base unit and a handset of a cordless telephone, including the step of transmitting a frame including a speech data portion, and a non-speech data portion. In one particular example, the size of the speech data portion and the size of the non-speech data portion are variable.
In an alternative embodiment, a cordless telephone includes a base unit, including a codec adapted to convert analog speech data from a far end party to digital samples, a variable encoder adapted to encode the digital samples, and a transceiver adapted to transmit and receive encoded digital samples. The cordless telephone also includes a handset, including a transceiver adapted to transmit and receive encoded digital samples, a controller adapted to act on non-speech data, and a transducer adapted to be responsive to speech data. According to this embodiment, the variable encoder is adapted to encode a speech data portion of a frame based upon a non-speech data portion of the frame.
In another alternative embodiment, a frame structure for digital RF communications between a base unit and a handset of a cordless telephone includes a speech data portion, and a non-speech data portion. In one particular example a size of the speech data portion and a size of the non-speech data portion are variable.